A disk drive, such as a magnetic disk drive, comprises a magnetic disk, spindle motor, magnetic head, and carriage assembly. The magnetic disk is disposed in a case. The spindle motor supports and rotates the disk. The magnetic head reads data from and writes data to the disk. The carriage assembly supports the head for movement relative to the disk. A head section of the magnetic head comprises a recording head for writing and a reproduction head for reading.
Magnetic heads for perpendicular magnetic recording have recently been proposed in order to increase the recording density and capacity of a magnetic disk drive or reduce its size. In one such magnetic head, a recording head comprises a main pole configured to produce a perpendicular magnetic field, return or write/shield pole, and coil. The return pole is located on the trailing side of the main pole with a write gap therebetween and configured to close a magnetic path that leads to a magnetic disk. The coil serves to pass magnetic flux through the main pole.
In order to improve the recording density, a high-frequency magnetic field assisted recording head is proposed, in which a spin-torque oscillator for use as a high-frequency oscillatory element is disposed between main and return poles and a high-frequency magnetic field from the spin-torque oscillator is applied to a magnetic recording layer. This magnetic head is constructed so that its gap magnetic field is enlarged by reducing the distance between the respective facing surfaces of the main and return poles.
In the case of the magnetic head described above, however, the spin-torque oscillator is located close to the main and return poles. Therefore, magnetization rotation in the spin-torque oscillator is transmitted to the main and return poles and further propagates as spin waves to the entire film surface of the poles. Thereupon, a magnetic field opposite to the gap magnetic field for effectively causing the spin-torque oscillator to oscillate is produced. Thus, the gap magnetic field is reduced by the produced magnetic field, so that satisfactory oscillation is prevented. Consequently, the high-frequency magnetic field for achieving magnetization reversal of the recording layer of a perpendicular recording medium is not sufficiently strong, so that the recorded signal quality is poor.